Coil construction for electronic timepieces

ABSTRACT

An electronic timepiece provided with a pair of spaced balance wheels mounted on a common shaft and carrying a magnetic circuit including an air gap between said balance wheels is provided with a coil having a streamlined periphery, or with a coil-holding member having said streamlined periphery.

United States Patent [191 Kurita et al.

[451 Mar. 26, 1974 COIL CONSTRUCTION FOR ELECTRONIC TIMEPIECESInventors: Hirohisa Kurita, Shimosuwa-machi;

Tomio Ota, Okaya, both of Japan Assignee:

Tokyo, Japan Filed:

Appl. No.: 319,1 10

Dec. 29, 1972 Foreign Application Priority Data Dec. 29, 1971 Japan46-001876 us. c|.. .,s gs 531(136 Int. Cl. G04c 3/04 Field of Search58/28 R, 28 A, 107;

Kabushiki Kaisha Suwa Seikosha,

[56] References Cited UNITED STATES PATENTS 2,986,683 5/1961 Lavet et al310/36 X 3,184,669 5/1955 Williams 310/36 X Primary ExaminerRichard B.Wilkinson Assistant Examiner-Edith Simmons Jackmon Attorney, Agent, orFirm-Blum, Moscovitz, Friedman & Kaplan [5 7] ABSTRACT An electronictimepiece provided with a pair of spaced balance wheels mounted on acommon shaft and carrying a magnetic circuit including an air gapbetween said balance wheels is provided with a coil having a streamlinedperiphery, or with a coil-holding member having said streamlinedperiphery.

2 Claims, 7 Drawing Figures COIL CONSTRUCTION FOR ELECTRONIC TIMEPIECESBACKGROUND OF THE INVENTION This invention relates to driving anddetecting coils for electronic timepieces, and in particular forelectronic timepieces having a balance driven by electromagnetic forcedue to the cooperation of said driving coil and permanent magnetsmounted on said balance.

Such electronic timepieces are generally provided with a magneticcircuit mounted on the balance having an air gap within which the coilsare positioned. This construction is required to insure stable operationof the timepiece. The gap between the permanent magnets and the coilsmust be as small as possible, both for efficient operation and in orderto provide an extremely thin timepiece. However, conventional circularcoils are characterized by an isochronous error caused by air resistancedue-to turbulent flow during the oscillation of the balance. Thearrangement in accordance with the invention seeks to avoid this defect.

SUMMARY OF THE INVENTION Generally speaking, in accordance with theinvention, an electronic timepiece is provided having a pair of balancewheels, a common shaft supporting said balance wheels in spaced relationfor oscillation thereof as a unit, and a pair of permanent magnets, saidpermanent magnets being mounted on the opposed faces of said balancewheels with an air gap therebetween. Either a coil having a streamlinedperiphery or a coilholding member bearing a coil, said coil-holdingmember having a streamlined periphery, is mounted in said gap.

Accordingly, an object of the invention is to provide a coil structurewhich minimizes air resistance caused by turbulent flow, and thereforeisochronous error.

The invention accordingly comprises the features of construction,combination of elements, and arrangement of parts which will beexemplified in the constructions hereinafter set forth, and the scope ofthe invention will be indicated in the claims.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed, and all statements of the scope of the invention which, as amatter of language, might be said to fall therebetween.

BRIEF DESCRIPTION OF THE DRAWINGS For a fuller understanding of theinvention, reference is bad to the following description taken inconnection with the accompanying drawings, in which:

FIG. 1 is a cross sectional view of a conventional balance wheel-coilarrangement for anelectronic timepiece taken along lines 1-1 of FIG. 2;

FIG. 2 is a top plan view of the conventional balance wheel-coilarrangement of FIG. 1;

FIG. 3 is a cross sectional view of a coil structure in accordance withthe invention;

FIG. '4 is a cross sectional view of a balance wheelcoil arrangement inaccordance with the invention;

FIG. 5 is a cross sectionaI v-iew of a second embodiment of a balancewheel-coil arrangement in accordance with the invention taken alonglines 55 of FIG. 6;

FIG. 6 is a top plan view of the balance wheel-coil arrangement of FIG.5; and

' FIG. 7 is a graphical representation of amplitude versus isochronismfor the conventional coil construction and the construction inaccordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIGS. 1 and 2,the conventional balance wheel-coil arrangement in accordance with theinvention is depicted. This arrangement consists of a pair of balancewheels I mounted in spaced relation on a common shaft. A first pair ofpermanent magnets 2 are mounted on the under surface of the upper platewhile a second pair of permanent magnets 3 are mounted on the uppersurface of the lower plate. The permanent magnets 2 and 3 are aligned infacing relation and are of a polarity such that a magnetic circuit isdefined therebetween with a magnetic field passing through the gapbetween the facing permanent magnets. A coil structure 4. incorporatingboth a detecting coil and a driving coil in a single cylindrical body ismounted on a coil support 5, said coil support being mounted to the baseplate (not shown) of the watch by means of a screw 6. Balancing weights7 are also mounted on balance wheels 1 on the sides thereof oppositepermanent magnets 2 and 3.

The arrangement of FIGS. 1 and 2 is characterized by turbulent flowcaused by air resistance. This in turn causes an isochronous error orpositional error as shown by graph A of FIG. 7.

The arrangement in accordance with the invention for avoiding such erroris depicted in FIG. 3, where it is seen that the coil structure 14 isprovided with a streamlined cross section by reason of a tapered periphery. This arrangement substantially reduces isochronous andpositional error, without regard to the orientation of the timepiece, asshown by graph B of FIG. 7. In the preferred embodiment, the peripheryof the coil member has an essentially V-shaped crosssection. The coilstructure of FIG. 3 is depicted mounted in a balance arrangement in FIG.4, wherein balance wheels 11 are mounted in spaced relation on a commonshaft and support permanent magnets 12 and 13 ofa construction similarto those of FIGS. 1 and 2..The coil'structure 14 is supported in the gapbetween said permanent magnets by a coil support 15, adapted formounting on the watch plate by a screw 16. The streamlined periphery ofcoil structure 14 substantially reduces air resistance and turbulence inthe region of the magnetic field. Balance weights 17 are also mounted onthe balance wheels 11.

A second embodiment of the arrangement in accordance with theinventionis depicted in FIGS. 5 and 6, wherein a conventionalcylindrical coil structure is mounted on a coil holder having astreamlined periphery at least in the region of the magnetic field ofthe permanent magnets 22, 23 mounted on balance wheels 21. Specifically,coil structure 24 is supported by a coil support 25 adapted for mountingon the base plate of the watch by screws 26, balancing weights 27 beingmounted on the balance wheels in the conventional manner. Thearrangement of FIGS. 5 and 6 offers the further advantage of providingfurther support for the coil as well as producing the streamlined effectwhich reduces turbulence.

The arrangement in accordance with the invention permits theconstruction of a thin, movable magnettype of balance having extremelystable oscillation characteristics.

It will thus be seen that the objects set forth above, and those madeapparent from the preceding description, are efficiently attained and,since certain changes may be made in the above constructions withoutdeparting from the spirit and scope of the invention, it is intendedthat all matter contained in the above description or shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed, and all statements of the scope of the invention which, as amatter of language, might be said to fall therebetween.

What is claimed is:

1. In an electronic timepiece having a balance construction formed witha pair of balance wheels mounted in spaced relation on a common shaftfor rotational oscillation, and having permanent magnet means mounted onthe facing surfaces of said balance wheels to define a magnetic circuithaving a gap between said permanent magnets through which magnetic fluxpasses, the improvement which comprises a coil construction formed witha tapered periphery, said tapered periphery of said coil constructionhaving an essentially V-shaped cross-section, said coil constructionbeing mounted at least in part 2. In an electronic timepiece having abalance construction formed with a pair of balance wheels mounted inspaced relation on a common shaft for rotational oscillation, and havingpermanent magnet means mounted on the facing surfaces of said balancewheels to define a magnetic circuit having a gap between said permanentmagnets through which magnetic flux passes,- the improvement whichcomprises a coil assembly; and a coil support supporting said coilassembly at least in part in said gap in said magnetic circult, saidcoil support extending about at least the portion of the circumferentialperiphery of said coil assembly in said gap, the portion of said coilsupport extending about the portion of the periphery of said coilassembly in said gap being tapered and having an essentially V-shapedcross-section.

1. In an electronic timepiece having a balance construction formed witha pair of balance wheels mounted in spaced relation on a common shaftfor rotational oscillation, and having permanent magnet means mounted onthe facing surfaces of said balance wheels to define a magnetic circuithaving a gap between said permanent magnets through which magnetic fluxpasses, the improvement which comprises a coil construction formed witha tapered periphery, said tapered periphery of said coil constructionhaving an essentially V-shaped cross-section, said coil constructionbeing mounted at least in part
 2. In an electronic timepiece having abalance construction formed with a pair of balance wheels mounted inspaced relation on a common shaft for rotational oscillation, and havingpermanent magnet means mounted on the facing surfaces of said balancewheels to define a magnetic circuit having a gap between said permanentmagnets through which magnetic flux passes, the improvement whichcomprises a coil assembly; and a coil support supporting said coilassembly at least in part in said gap in said magnetic circuit, saidcoil support extending about at least the portion of the circumferentialperiphery of said coil assembly in said gap, the portion of said coilsupport extending about the portion of the periphery of said coilassembly in said gap being tapered and having an essentially V-shapedcross-section.